Whole Foods is stealing Walmart and Trader Joe's customers with its low prices

Foot traffic to Amazon's new grocery store jumped 17% during the week that Whole Foods cut its prices, compared to the same week a year earlier, according to data analytics firm Thasos Group.

Walmart(WMT) and Kroger(KR) accounted for a combined 40% of new customers to Whole Foods between August 28 to September 3. Regular shoppers of Sprouts and Target also shifted loyalty, but it was Trader Joe's that was hit the hardest: Nearly 10% of its regular customers went to Whole Foods that week.

After completing its $13.7 billion purchase of Whole Foods in late August, Amazon(AMZN) slashed the prices of dozens of items at all 460 of its new grocery stores. From fresh fish to produce, prices were down across the board.